/*
 * Copyright (c) Kumo Inc. and affiliates.
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <melon/fingerprint.h>

#include <melon/portability.h>
#include <melon/utility.h>
#include <melon/detail/fingerprint_polynomial.h>

#include <utility>

namespace melon {
    namespace detail {
        namespace {
            // The polynomials below were generated by a separate program that requires the
            // NTL (Number Theory Library) from http://www.shoup.net/ntl/
            //
            // Briefly: randomly generate a polynomial of degree D, test for
            // irreducibility, repeat until you find an irreducible polynomial
            // (roughly 1/D of all polynomials of degree D are irreducible, so
            // this will succeed in D/2 tries on average; D is small (64..128) so
            // this simple method works well)
            //
            // DO NOT REPLACE THE POLYNOMIALS USED, EVER, as that would change the value
            // of every single fingerprint in existence.
            template<size_t Deg>
            struct FingerprintTablePoly;

            template<>
            struct FingerprintTablePoly<63> {
                static constexpr uint64_t data[1] = {0xbf3736b51869e9b7};
            };

            template<>
            struct FingerprintTablePoly<95> {
                static constexpr uint64_t data[2] = {0x51555cb0aa8d39c3, 0xb679ec3700000000};
            };

            template<>
            struct FingerprintTablePoly<127> {
                static constexpr uint64_t data[2] = {0xc91bff9b8768b51b, 0x8c5d5853bd77b0d3};
            };

            template<typename D, size_t S0, size_t... I0>
            constexpr auto copy_table(D const (&table)[S0], std::index_sequence<I0...>) {
                using array = std::array<D, S0>;
                return array{{table[I0]...}};
            }

            template<typename D, size_t S0>
            constexpr auto copy_table(D const (&table)[S0]) {
                return copy_table(table, std::make_index_sequence<S0>{});
            }

            template<typename D, size_t S0, size_t S1, size_t... I0>
            constexpr auto copy_table(
                D const (&table)[S0][S1], std::index_sequence<I0...>) {
                using array = std::array<std::array<D, S1>, S0>;
                return array{{copy_table(table[I0])...}};
            }

            template<typename D, size_t S0, size_t S1>
            constexpr auto copy_table(D const (&table)[S0][S1]) {
                return copy_table(table, std::make_index_sequence<S0>{});
            }

            template<typename D, size_t S0, size_t S1, size_t S2, size_t... I0>
            constexpr auto copy_table(
                D const (&table)[S0][S1][S2], std::index_sequence<I0...>) {
                using array = std::array<std::array<std::array<D, S2>, S1>, S0>;
                return array{{copy_table(table[I0])...}};
            }

            template<typename D, size_t S0, size_t S1, size_t S2>
            constexpr auto copy_table(D const (&table)[S0][S1][S2]) {
                return copy_table(table, std::make_index_sequence<S0>{});
            }

            template<size_t Deg>
            constexpr poly_table<Deg> make_poly_table() {
                FingerprintPolynomial<Deg> poly(FingerprintTablePoly<Deg>::data);
                uint64_t table[8][256][poly_size(Deg)] = {};
                // table[i][q] is Q(X) * X^(k+8*i) mod P(X),
                // where k is the number of bits in the fingerprint (and deg(P)) and
                // Q(X) = q7*X^7 + q6*X^6 + ... + q1*X + q0 is a degree-7 polynomial
                // whose coefficients are the bits of q.
                for (uint16_t x = 0; x < 256; x++) {
                    FingerprintPolynomial<Deg> t;
                    t.setHigh8Bits(uint8_t(x));
                    for (auto &entry: table) {
                        t.mulXkmod(8, poly);
                        for (size_t j = 0; j < poly_size(Deg); ++j) {
                            entry[x][j] = t.get(j);
                        }
                    }
                }
                return copy_table(table);
            }

            // private global variables marked constexpr to enforce that make_poly_table is
            // really invoked at constexpr time, which would not otherwise be guaranteed
            MELON_STORAGE_CONSTEXPR auto const poly_table_63 = make_poly_table<63>();
            MELON_STORAGE_CONSTEXPR auto const poly_table_95 = make_poly_table<95>();
            MELON_STORAGE_CONSTEXPR auto const poly_table_127 = make_poly_table<127>();
        } // namespace

        template<>
        const uint64_t FingerprintTable<64>::poly[poly_size(64)] = {
            FingerprintTablePoly<63>::data[0]
        };
        template<>
        const uint64_t FingerprintTable<96>::poly[poly_size(96)] = {
            FingerprintTablePoly<95>::data[0], FingerprintTablePoly<95>::data[1]
        };
        template<>
        const uint64_t FingerprintTable<128>::poly[poly_size(128)] = {
            FingerprintTablePoly<127>::data[0], FingerprintTablePoly<127>::data[1]
        };

        template<>
        const poly_table<64> FingerprintTable<64>::table = poly_table_63;
        template<>
        const poly_table<96> FingerprintTable<96>::table = poly_table_95;
        template<>
        const poly_table<128> FingerprintTable<128>::table = poly_table_127;
    } // namespace detail
} // namespace melon
